From going through the terms of service on Khan Academy, I found 10.3, which stated
"As discussed herein, Khan Academy does not permit copyright, trademarks, or other intellectual property infringing activities on the Services, and will terminate access to the Services, and remove all User Content or other content submitted, by any Users who are found to be repeat infringers."
I have come across TONS of programs by some famous programmers and some not so famous programmers that says "Copyright 2020 by ..." or "©...". I'm pretty sure to the above statement that this is disallowed, so here is my proposal:
I know the KA team has automatic flags for things like "/cs/pro/5733417664643072", so I suggest they make another one — for "copyright" or "©". This can help make sure newer users don't do the wrong things, and older users can set an example for the newer users.
Besides, it's copyright infringement to say "copyright" when you haven't copyrighted it.